1D versus 2D Growth of Soluble Acene Crystals from Soluble Acene/Polymer Blends Governed by a Residual Solvent Reservoir in a Phase-Separated Polymer Matrix

The growth mechanism of soluble acene is highly dependent on the remaining residual solvent following solution processing. The relationship between the amount of residual solvent and the growth modes of a prototypical soluble acene, 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-pentacene) are examined under spin casting TIPS-pentacene/insulating polymer blends. Changing spin time of the blend solution allows to control the amount of residual solvent, which significantly determines the growth modes of TIPS-pentacene vertically segregated onto the insulating polymer. In situ observation of crystal growth reveals that excess residual solvent in short spin time induces a convective flow in a drying droplet, thereby resulting in 1D growth of TIPS-pentacene crystals. On the other hand, optimal amount of residual solvent in a moderate spin time results in 2D growth of TIPS-pentacene crystals. The well-developed 2D spherulites allow for higher field-effect mobility than that of the 1D crystals because of the higher perfectness and coverage of TIPS-pentacene crystals. The use of other types of soluble acene and insulating polymer only changes the kinetics of crystallization, while the transition of growth mode from 1D to 2D is still observed. This general growth mechanism facilitates the understanding of crystallization behavior of soluble acene for the development of high-performance organic transistors.